1. Field of the Invention
The present invention relates to a common rail type fuel injection system. Specifically, the present invention relates to a technology for detecting an abnormality in a pressure on an inlet side of a supply pump or an inlet side of a high-pressure pump included in the supply pump.
2. Description of the Related Art
A common rail type fuel injection system pressure-feeds fuel from a fuel tank into a common rail with the use of a supply pump and accumulates the fuel in the common rail. The system injects the fuel, which is accumulated in the common rail, from injectors.
The supply pump includes a high-pressure pump, which pressurizes the fuel to a high pressure and pressure-feeds the fuel, and a feed pump, which draws the fuel from an outside and feeds the fuel to the high-pressure fuel.
An assist pump for supplying the fuel to the supply pump is mounted in the common rail type fuel injection system if the fuel tank is disposed away from the supply pump or if a vertical interval between the fuel tank and the supply pump is large.
Usually, a fuel filter is disposed in a fuel supply pipe, through which the fuel is supplied from the fuel tank to the supply pump. Thus, the fuel flowing through the fuel supply pipe is filtered and supplied to the supply pump.
Conventionally, the common rail type fuel injection system is not equipped with means for sensing an inlet pressure, or a fuel pressure at an inlet of the supply pump or at an inlet of the high-pressure pump. Therefore, the inlet pressure of the supply pump or the high-pressure pump is not controlled.
Some abnormalities such as a high pressure abnormality or a low pressure abnormality can occur in the inlet pressure of the supply pump because of excessive pressure-feeding operation or defective pressure-feeding operation of the assist pump or clogging of the fuel filter.
Likewise, some abnormalities such as a high pressure abnormality or a low pressure abnormality can occur in the inlet pressure of the high-pressure pump because of defective pressure-feeding operation of the feed pump or a failure in a regulator valve.
If the high pressure abnormality occurs in the inlet pressure of the supply pump, the high pressure abnormality occurs in the supply pump. In such a case, there is a possibility that failures are caused in fuel sealing portions inside the supply pump or in fuel sealing portions of various parts downstream of the supply pump.
If the low pressure abnormality occurs in the inlet pressure of the supply pump, there is a possibility that cavities are generated inside the supply pump.
In order to perform injection control highly accurately, a common rail pressure has to be controlled highly accurately. Therefore, the inlet pressure of the supply pump, which affects the common rail pressure, has to be limited within a narrow range and used.